When the draw bar of a railroad car, such as a transit car, is not attached to another car and is therefore unused for a period of time while the car itself is being used, the draw bar apparatus can swing freely about its normal vertical pivot axis unless a restraint system is provided. After a period of non-use, the draw bar can end up in any of a variety of positions, unpredictably, thus complicating the task of coupling that draw bar to another. Although various gathering devices have been developed, none can accommodate the possible extremes in combinations of draw bar position and track curvature which can occur.
For this reason, various centering devices have been developed. Generally, these devices use some combination of springs with levers, cam surfaces or torque systems to urge the draw bar toward its central position. It is characteristic of these that the restoring force on the draw bar be exerted whenever the draw bar departs significantly from its center position and that force usually increases as the angular departure from center increases.
While these devices work well on an unused draw bar, they are not removed or deactivated when the draw bar is coupled to another car and, therefore, continue to exert a restraining or restoring force on the draw bar as the coupled cars pass around a curve. This is an undesirable situation because desirable angular movement is impeded.